Autoimmune diseases are widespread and have been the subject of considerable attention in attempts to develop an understanding of the diseases themselves and in attempts to develop therapies. The most common approach to treating autoimmune diseases and other immunopathologies is general immunosuppression. Immunosuppression has the obvious disadvantage of crippling the ability of the subject to respond to materials which are truly foreign and against which an immune response is truly needed. A slightly more sophisticated approach relies on the removal of antibodies or immune complexes involving the target tissue. This approach is difficult to accomplish, however, and has adverse side effects as well.
Investigations of further approaches have included studies related to the role of cell membranes. Polyunsaturated fatty acids in cell membranes, for example, are known to be critical to the immune function. Polyunsaturated fatty acids of particular interest are the eicosanoids, which are the metabolites of arachidonic acid (5,8, 11,14-eicosatetraenoic acid, referred to variously herein as 20:4(5,8,11,14)and 20:4(n-6)). Eicosanoids modulate the immune system either directly by stimulating target cells or indirectly by modulating the production of other soluble regulatory factors such as tumor necrosis factor and cytokines.
There have been attempts to control autoimmunity by substituting other fatty acids for arachidonic acid. The substitutes have primarily been fatty acids of the n-3 type, such as .gamma.-1inolenic acid (9,12,15-octadecatrienoic acid, or 18:3(9,12,15))and fish oils, which are a source of n-3 fatty acids. Unfortunately, these are efficacious only at very high levels, and compete poorly with the arachidonic acid which is otherwise present in human diets. Furthermore, these substitutes are particularly ineffective in replacing the eicosanoid content of the phosphatidyl inositols, which are a critical class of lipids. As a result, this approach has not met with success, and no useful data confirming its viability has been reported.